This application claims the priority of PCT International Application No. PCT/EP00/08329, filed 26 Aug. 2000 and German Patent Document 199 44 075.1, filed 14 Sep. 1999, the disclosure of which is expressly incorporated by reference herein.
The invention is related to a method for monitoring and forecasting traffic conditions in a traffic network (particularly a road network) with effective bottlenecks. As used herein, the phrase xe2x80x9ceffective bottlenecksxe2x80x9d is to be understood to include both bottlenecks in the actual sense, (a reduction in the number of usable lanes), and bottlenecks in the broader sense, such as are caused, for example, by one or more incoming feeder lanes, a bend, a grade, a downgrade, a division of a lane into two or more lanes, one or more exits or a bottleneck moving slowly (by comparison with the average vehicle speed in free traffic), for example owing to a vehicle which is being driven slowly.
Various methods for monitoring and forecasting traffic conditions of this generic type are known, and are of particular interest also for diverse telematics applications in vehicles. One aim of these methods is to obtain, from measured traffic data detected at traffic measuring points, a qualitative description of the traffic state at the respective measuring point and its surroundings. Measuring points in this sense include both those installed in a stationary fashion on the route network, and moveable measuring points such as, for example, sample vehicles moving in the traffic (so-called xe2x80x9cfloating carsxe2x80x9d) or by a measurement of the traffic flow obtained by means of monitoring from deep space, space or the air.
For the purpose of qualitative description of the traffic state, it is known to divide the latter into various phases, for example into a phase of xe2x80x9cfree trafficxe2x80x9d, in which relatively fast vehicles can overtake without a problem, a phase of xe2x80x9csynchronized trafficxe2x80x9d, in which possibilities for overtaking scarcely exist, but a high traffic intensity still prevails, and a phase of xe2x80x9ccongestionxe2x80x9d, in the case of which the vehicles are virtually stationary and also the traffic intensity drops to very low values. (See, for example, the journal article by B. S. Kerner and H. Rehborn, xe2x80x9cExperimental properties of complexity in traffic flowxe2x80x9d, Physical Review E 53, R 4275, 1996.) As used herein, xe2x80x9csynchronized trafficxe2x80x9d is to be understood both as a state in which, because there are scarcely any possibilities of overtaking, all vehicles in different lanes are driven at a very similar, xe2x80x9csynchronizedxe2x80x9d speed, (for example on route sections without approach roads and exits), and a traffic state in which the distribution of speed for the vehicles in different lanes can differ, but there is a tendency for synchronization of the speeds of those vehicles in different lanes which are respectively being driven on an identical route, since there are scarcely any possibilities of overtaking with reference to one driving route.
The phase division is based on the idea of selecting the phases such that each of them corresponds to specific characteristic properties of the traffic flow, making it possible to estimate the temporal and spatial extent of route sections in which the traffic state is in a specific phase. In the journal article by B. S. Kerner, xe2x80x9cExperimental Features of Self-Organization in Traffic Flowxe2x80x9d, Physical Review Letters, Vol. 81, No. 17, page 3797, so called xe2x80x9cpinch regionsxe2x80x9d (regions of xe2x80x9ccongested synchronized trafficxe2x80x9d) are selected in the phase of xe2x80x9csynchronized trafficxe2x80x9d, and are subsequently treated specially. These are regions inside synchronized traffic in which it is possible to drive only at very low speeds and in which there is spontaneous formation of short-lived congestion states which can migrate upstream and grow in the process, and which can then possibly lead to a lasting congestion state.
Various methods are already known for monitoring and predicting traffic xe2x80x9ccongestion pointsxe2x80x9d (frequently called a xe2x80x9cmoving jamxe2x80x9d). See, for example, the automatic congestion dynamics analysis described in German patent document DE 196 47 127 A1, whose content is incorporated herein by reference, and methods known from the literature mentioned there.
In German patent document 198 35 979.9, which is not a prior publication, there is, moreover, a description of the monitoring and forecasting of synchronized traffic, in particular the detection of a phase transition between free and synchronized traffic, and a prediction of the spatial extent of synchronized traffic. This is done by inferring the position of an upstream edge of the latter based on the fact that, at a corresponding upstream measuring point, specific conditions for an induced upstream phase transition from free to synchronized traffic are no longer fulfilled, or widespread congestion has arisen. This method is particularly suitable for detecting the start of a phase of synchronized traffic at an effective bottleneck of the traffic network, and for tracking the temporal development of the synchronized traffic forming upstream of this bottleneck, the downstream edge of which generally remains fixed at the effective bottleneck. An edge fixed at the effective bottleneck is understood in this case as one which remains in the surroundings of this bottleneck. That is, it remains essentially stationary in the surroundings of a stationary effective bottleneck, or moves along essentially synchronously with a moveable effective bottleneck. The location of the effective bottleneck is therefore the one where the downstream edge of the synchronized traffic is momentarily located.
In a related, co-pending German patent application the current traffic conditions are monitored with regard to different state phases, particularly synchronized traffic and a pinch region as well as the phase transition between states of synchronized traffic on the one hand, and free traffic, on the other hand. The future traffic state is predicted on this basis, if required. In particular, this method can be used to estimate the edges of regions of synchronized traffic relatively accurately for current points in time, or to predict future points in time at which such edges are not (or will not be) located at a measuring point, but somewhere between two measuring points. Suitably designed fuzzy logic is preferably used in this case.
In German patent document DE 199 44 077 A1, (not prior art) the current traffic state is monitored with regard to different state phases and, in particular, with regard to synchronized traffic and a pinch region as well as the phase transition between states of synchronized traffic, on the one hand, and free traffic, on the other hand. The future traffic state is predicted on this basis, if required. In particular, this method can be used to estimate the edges of regions of synchronized traffic relatively accurately for current points in time or to predict future points in time at which such edges are not (or will not be) located at a measuring point, but somewhere between two measuring points. A suitably designed fuzzy logic is preferably used in this case.
European patent document EP 0 884 708 A2 discloses a method for predicting traffic conditions in a traffic network having nodes and edges running therebetween. Detection data referring to the current traffic are acquired and transmitted to a control center which uses them to describe the current traffic state on the traffic network in the form of respective traffic phases which represent the state on an edge or an edge section. It predicts the traffic state by calculating at least the movements and future positions of the traffic phases. The phases are described in binary fashion in the form of the phases of xe2x80x9cfreexe2x80x9d and xe2x80x9ccongestedxe2x80x9d; in the five phases of xe2x80x9cfreexe2x80x9d, xe2x80x9cbusyxe2x80x9d, xe2x80x9cdensexe2x80x9d, xe2x80x9csluggishxe2x80x9d and xe2x80x9ccongestedxe2x80x9d; or by using another number of different phases. For prediction, use is made of phase boundary speeds which, for example, are calculated by linear regression with the aid of current and earlier detection data, or as the quotient of the difference between the incoming and departing flow at the phase boundary and the difference between the vehicle density upstream and downstream of the phase boundary.
One object of the invention is to provide a method for reliably monitoring the current traffic state, specifically even in a region upstream of effective bottlenecks, and for reliably predicting the future traffic state.
This and other objects and advantages are achieved by the method according to the invention, in which the traffic state upstream of an effective bottleneck is classified to a particular pattern of dense traffic, whenever an edge fixed at the relevant effective bottleneck is detected between downstream free traffic and upstream synchronized traffic (that is, when dense traffic forms upstream of the bottleneck). The pattern classification of the traffic state includes a division of the traffic upstream of the bottleneck into one or more consecutive upstream regions of different state phase composition. Moreover, the pattern classification includes a profile, dependent on state phase, time and location, of traffic parameters taken into account for the state phase determination, such as average vehicle speed, traffic flow and/or traffic density.
In the case of increasing traffic, and specifically at effective bottlenecks (which may be primarily stationary bottlenecks, but in some incidences may include moveable bottlenecks such as very slowly moving road-construction or road-maintenance vehicles or migrating building sites), a formerly free traffic state will frequently be initially transformed into a so-called region of synchronized traffic upstream of the bottleneck, whilst resulting (depending on further traffic) in a pattern, typical of the bottleneck, of dense traffic. In the minimum version, this pattern may comprise only the region of synchronized traffic adjoining the effective bottleneck upstream. The formation of a pinch region is also observed in the case of increasing traffic volume and/or appropriate route infrastructure. Congestion points can develop from this pinch region and propagate upstream, since it is possible for free or synchronized traffic or a pinch region to be present between each two congestion points. The region in which the widespread congestion propagates upstream (by contrast with the localized congestion occurring in pinch regions) is denoted as a region of xe2x80x9cmoving widespread congestionxe2x80x9d (See e.g, B. S. Kerner, xe2x80x9cExperimental features of the emergence of moving jams in free flow traffic, J. of Physics A: Mathematical and General, vol. 33, pp L221-L228 (2000).)
As a result of these findings, in the case of detection of synchronized traffic moving upstream of a bottleneck the method according to the invention makes it possible to use comparatively fewer current or predicted measured traffic data to assign the traffic state to a fitting pattern typical of the respective bottleneck. Further analysis or evaluation and also prediction of the future traffic state can then be performed on the basis of this pattern recognition with the aid of comparatively little data material which is to be processed, and consequently with correspondingly slight computation outlay. A further essential advantage of this method is that, by contrast with mathematical traffic state models with many parameters to be validated, it includes a pattern-based modeling without parameters to be validated.
One embodiment of the invention permits the pattern classification of the traffic state even when a pattern, arising initially at an effective bottleneck, of dense traffic has extended beyond one or more further, upstream effective bottlenecks. The overarching pattern is built up from the same regions as an individual pattern including only one effective bottleneck. That is, the overarching pattern also comprises the characteristics of regions of xe2x80x9csynchronized trafficxe2x80x9d, xe2x80x9cpinch regionsxe2x80x9d and xe2x80x9cmoving widespread congestionxe2x80x9d.
According to a feature of the invention, the pattern determined as a function of time and location for a respective bottleneck is determined empirically from recorded traffic measured data and stored in a fashion which can be called up. As a result, it is possible at any later point in time at which a fixed edge is detected at the bottleneck between downstream free traffic and upstream synchronized traffic, to select the pattern profile which best fits the measured traffic data currently recorded or predicted for the relevant point in time from the stored pattern profiles. The latter can be used as a current or predicted traffic state for the corresponding route section of the traffic network upstream of the bottleneck.
In another embodiment of the invention, a dense traffic state upstream of an effective bottleneck is distinguished as a function of vehicle influx in accordance with three pattern variants, and each of the three variants is assigned a corresponding time- and location-dependent pattern profile for one or more of the important traffic parameters of xe2x80x9cmean vehicle speedxe2x80x9d, xe2x80x9ctraffic flowxe2x80x9d and xe2x80x9ctraffic densityxe2x80x9d. In a first variant, the pattern comprises only one region of synchronized traffic. In a second variant, the pattern additionally comprises a pinch region adjoining upstream, and in a third pattern variant there is in addition a region of moving widespread congestion upstream of the pinch region. The associated, generally time-dependent edge positions between the various pattern regions are determined by respectively suitable methods, for example of the type mentioned at the beginning.
Still another embodiment of the invention permits the detection and tracking of overarching patterns of dense traffic in the considered traffic network as a function of the vehicle flows. In particular, the location and time of the resolution of a respective overarching pattern and the sequence of the individual regions of xe2x80x9csynchronized trafficxe2x80x9d, xe2x80x9cpinch regionxe2x80x9d and xe2x80x9cmoving widespread congestionxe2x80x9d can be determined in each overarching pattern as a function of the vehicle flows. Moreover, the temporal and spatial characteristic of congestion points propagating upstream by means of regions of synchronized traffic and/or pinch regions can be predicted when a region of xe2x80x9cmoving widespread congestionxe2x80x9d overlaps in an overarching pattern with regions of synchronized traffic and/or pinch regions.
A further refinement of this measure of determining the edge position includes a temporal tracking of the positions of diverse edges between the various pattern regions and/or congestion points in overarching patterns and/or the detection of newly occurring overarching patterns, so that the position and extent of each of the regions (which differ in their state phase composition) of an individual or overarching pattern can be tracked in temporal development.
In still another embodiment of the invention, the expected travel time required for traversing the route section in which the individual or overarching pattern of the dense traffic is located is additionally determined as a function of time and stored. The stored travel time information can be used, for example, directly within the framework of a method for estimating travel times, currently to be expected or to be expected in future for prediction, for travelling specific, prescribable routes of the traffic network.
Finally, according to still another embodiment of the invention, the positions of associated edges and the influx to the pattern are detected currently after detection of an individual or overarching pattern. This information is used to select the pattern profile which best fits therewith from the stored pattern profiles, and to carry out a prediction on the further development of the pattern of dense traffic at the relevant effective bottleneck. This can comprise, in particular, a prediction of relevant traffic state parameters such as average vehicle speed, traffic flow and/or traffic density and, if required, also be travel time to be expected.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.